Positional control system for photoscanner



June 30, 1959 w. P. FRANTZ POSITIONAL CONTROL SYSTEM FOR PHOTOSCANNERFiled April 10, 1956 2 Sheets-Sheet 1 NSFUSANQ INVENTOR W/E/W F?/CiA/VTZ ATTORNEY www June 30, 1959 w. P. FRANTZ 2,892,948

POSITIONAL CONTROL SYSTEM FOR PHoToscANNER Filed April 10, 1956l 2SheetS-Sheeb 2 24 25 Z4' ,25 Z A t)A F l |j F I |l il vl C 17 l l E I llf VVVVVVVVVVVW I 5 lNvENroR q l/V/lgg/QTRF ,4A/TZ M ATTORNEY UnitedStates Patent() POSITIONAL CONTROL SYSTEM FOR PHOTOSCANNER Wilbert P.Frantz, Great Neck, N.Y., assignor to Sperry Rand Corporation, acorporation of Delaware Application April 10, 1956, Serial No. 577,401

20 Claims. (Cl. Z50-202) The invention relates to scanning systems, andin particular to a photoscanning system for scanning a chart and forautomatically positioning the photoscanner with respect to the chart bycomparing infomation derived while scanning with supplied positionaldata. This application is a continuation-in part of application SerialNo. 534,731, filed September 15, 1955, and abandoned on March 28, 1957.

In employing certain navigation systems, such as the loran system, tonavigate a craft, special charts of the area in which the craft is to benavigated are required. These charts display both a map of the area andfamilies of hyperbolic lines of position associated with the area. Thesehyperbolic or loran lines of position are lines of constant timedifference between the arrival of first recurrent pulses from a masterstation and second recurrent pulses from a slave station and each loranline is `numbered according to the corresponding time difference. Theintersection of a first line of position from one pair of transmittingstations and a second line of position from another pair of transmittingstations establishes a navigational fix on the chart. The loran receivermeasures the time differences between the arrivals of pulses from firstand second pairs of stations, and the intersection of the lines ofposition on the loran chart corresponding to the measured timedifferences establishes the crafts position.

The number of loran lines of position on a chart is determined by thesize of the chart and the interval of time difference desired betweenadjacent lines of position. Standard loran charts are printed in whichthe time diterence interval between adjacent lines of position may be20, 50, 100 microseconds. Where the time differences measured by theloran receiver do not coincide with an intersection of the printed loranlines of position on the chart, it is necessary for the operator ornavigator to locate the crafts position by interpolating betweenadjacent lines of position. As the position of the craft changes,different loran time difference measurements are obtained from the loranreceiver and newinterpolations must be made. This interpolation processis both tedious and time consuming, and results in the possibility ofhuman error in determining the position of the craft especially if theposition of the craft is changing rapidly and many measurements of timedifferences and many interpolations are required.

A pictorial indicator automatically indicating the position of the crafton a map at all times operating together with an automatic plotter fordisplaying the .track of the craft on the map would greatly relieve theburden of the navigator and enhance the accuracy and utility of theloran navigation system. To develop such an automatic loran craftposition plotter, it is necessary to solve the problem of moving anobject representing Vthe craft over the surface of a chart andautomatically positioning the 4object with respect to the lines on thechart when ,the

crafts position corresponds toa position between vthe ice lines. Thepresent invention is concerned with a solution to this problem.

A principal object of this invention is to provide apparatus forautomatically interpolating between two spaced lines on a chart.

Another object of the invention is to automatically position an objectwith respect to navigational lines of position on a chart in accordancewith supplied navigational data.

Yet another object of the invention is to automatically move aphotoscanner while scanning lines on a chart to a redetermined positionbetween two selected lines on a chart in accordance with suppliednavigational data.

Another object of the invention is to automatically control the angularposition of a shaft in accordance with the position of the center ofscan of a photoscanner.

Still another object of the invention is to produce an .output voltagewhose magnitude is related to the distance `between a line of positionon a chart and an imaginary line representing craft position.

A further object is to produce an output voltage whose magnitude isrelated to the distance between the center of scan of a photoscannertransversely scanning first and second lines on a chart and apredetermined position be,- tween the lines being scanned.

An additional object is to provide a photo-scanner producing recurrentoutput reference pulses whose time position corresponds to the center ofscan of the scanner.

ln accordance with the present invention there is introduced a scanningsystem including a photoscanner for transversely scanning first andsecond lines on a chart. A first direct voltage is produced by saidscanning system whose magnitude varies according to the distance betweenthe first and second lines being scanned as measured along the line ofscan. This first direct voltage is supplied to a Yvoltage divider whosedivision is determined by input data representing a predetermined lineof position on the chart between the first and second lines beingscanned. The voltage divider produces a second output voltage whosemagnitude represents the distance between one of the lines on the chartbeing scanned and an imaginary line on the chart corresponding to thepredetermined line of vposition as controlled by the input data. A thirddirect voltage is produced by the scanning system whose magnitude variesaccording to the distance between the center of scan of the photoscannerand one of the lines on the chart being scanned. A voltage comparatorresponsive to the difference between the second and third outputvoltages is employed to energize a servomotor to vary the position ofthe photoscanner along its direction of scan until the center of scan ofthe photoscanner coincides with the imaginary line on the chart betweenthe first and second lines.

In an alternative embodiment of the invention, the difference voltagefrom the voltage comparator is supplied vto a servomotor coupled to theshaft of a potentiometer .used as the voltage divider which produces thesecond `direct output voltage. The servomotor automatically varies theangular position of the shaft of the potentiometer until the magnitudeof the second direct voltage equals the magnitude of the third directvoltage. Under this condition, the angular position of the shaftcorresponds to the position of the center of scan of the photoscannerwith respect to the lines being scanned.

the phototube with an apertured mask covering the opening to thephotosensitive cathode and the magnetic pickotf for producing the centerof scan pulses; and

Fig. 3 illustrates waveforms of voltages associated with the blockdiagram of Fig. 1.

Referring to Fig. l, a photoscanner situated above chart 18 transverselyscans the lines a and b. The photoscanner includes a phototube 11 whosephotocathode is covered with a mask 14 having a long narrow apertureextending parallel to the longitudinal axis of the phototube, as shownin the exploded view of Fig. 2. The phototube 11 with mask 14 issituated within a hollow cylindrical drum 12 which has a one turnhelical slit 13 in the wall thereof. Light is admitted to thephotocathode only through the very small opening delined by theintersection of the narrow helical slit 13 and the narrow aperture 15 inmask 14. The cylindrical drum is rotated at a constant angular velocityby motor 16 to provide photoscanning along a straight line extendingparallel to the longitudinal axis of the cylindrical drum. The image oflines a and b is focused upon the photocathode of tube 11 by a lens 19.The photoscanner 10 is similar to the scanner shown in applicationSerial No. 473,249, filed December 6, 1954, in the name of Roger B.Williams, Ir., entitled Pulse Amplitude Equalizing System, and assignedto the same assignee as the present invention.

A magnetic tab 20 is attached to the outside wall of the cylindricaldrum 12 at a position thereon corresponding to the center of scan of thephotoscanner. As the cylindrical drum rotates at a constant angularvelocity, the magnetic tab 20 revolves past a pickup coil 21 and inducesa pulse voltage across the terminals thereof whose time position occursat the center of scan.

As photoscanner 10 transversely scans lines a and b, the phototube 11produces recurrent output pulses on lead 22 corresponding to the linesbeing scanned. These pulses are amplied and shaped in pulse ampliersystem 23 to produce recurrent output pulses of waveform A, illustratedin Fig. 3, in a manner substantially identical to that shown anddescribed in the aforesaid pending application S.N. 473,249. The timedifference between the recurrent pulses of waveform A varies accordingto the distance between lines a and b as measured along the line ofscan. Thus, the time difference between the recurrent pulses identifiedas 24, corresponding to the line a, and the recurrent pulses 25,corresponding to the line b, varies according to the distance betweenthese lines.

Photoscanner 10 is arranged to scan at least a total distance equal totwice the spacing between the lines, as measured along the line of scan.TheA lines a and b do not have to be parallel nor are they limited tostraight lines. More than the two lines shown may be scanned if desired.

The recurrent pulses of waveform A are coupled to a delay pulsegenerator 60 to produce the delayed output pulses of waveform B. Thesepulses are delayed only slightly from the pulses of waveform A. Thedelayed pulses of waveform B are applied to a sawtooth generator`26 forproducing a linear sawtooth voltage wave of waveform C. This linearsawtooth voltage wave has peak values corresponding to the time intervalbetween successive pulses. Accordingly, the peak value of the linearsawtooth voltage cycle generated between the pulses 24 and 25 variesaccording to the distance between the lines a and b, as measured alongthe line of scan. The sawtooth voltage wave of waveform C is coupled toa pair of electronic switches 36 and 61.

The center of scan pulses induced in pickup coil 21 are coupled overlead 27 to a pulse generator 28 which shapes the center of scan pulsesto produce recurrent narrow gating pulses of waveform D. These center of`scan pulses occur once each revolution of the photo- Cates zeropercent.

scanner. The center of scan pulses of waveform D are coupled toelectronic switch 36.

Both the recurrent pulses of waveform A and the center of scan pulses ofwaveform D are coupled to a bistable multivibrator 62. The center ofscan pulses activate or turn on the multivibrator, which is turned offby the first pulse of waveform A immediately following each activationof the pulse selector. In other words, multivibrator 62 is activated toproduce a rectangular output voltage whose leading edges coincide withthe recurrent center of scan pulses of waveform D and whose trailingedges coincide with the first pulses of waveform A. The rectangularoutput voltage from multivibrator 62 appears as waveform E in Fig. 3,and is supplied to a pulse generator 63 to produce recurrent outputpulses whose time of occurrence coincides with the trailing edges of therectangular voltage. Thus, the combination of bistable multivibrator 62and pulse generator 63 constitute a pulse selector which operates toselect and produce a pulse train as in waveform F simultaneously withthe rst pulses of waveform A following the pulses of waveform D. Therecurrent output pulses from pulse generator 63 are supplied to activateelectronic switch 61.

Electronic switch 61 is recurrently activated by the pulses of waveformF to periodically sample the magnitude of the linear sawtooth voltagewave. Electronic switch 61 charges condenser 64 to the instantaneousvalue of the sawtooth voltage wave at the instant of occurrence of thepulses of waveform F. Condenser 64 is charged to a voltage equal to thepeak value of the sawtooth voltage cycle generated during the intervalbetween pulses 24 and 25 of waveform A. Thus, condenser 64 produces afirst direct output voltage of waveform G whose magnitude represents thedistance between lines a and b as measured along the line of scan. Thisfirst direct voltage is coupled to a linear potentiometer voltagedivider 31. Potentiometer 31 may be of the continuously rotatable type.A secondl direct output voltage of waveform H is produced at the arm 32of potentiometer 31, of a magniutde determined by the setting or angularposition of shaft 33.

Electronic switch 36 is recurrently activated by the center of scanpulses of waveform D to periodically sarnple the magnitude of the linearsawtooth voltage wave. Electronic switch 36 charges condenser 37 to theinstantaneous value of the sawtooth voltage at the instant of occurrenceof the center of scan pulses. Condenser 37 produces a third directoutput voltage of waveform I whose magnitude represents the distancebetween line a on the chart and the position c on the chartcorresponding to the center of photoscanner 1t).

The magnitude of the second direct output voltage o waveform Hrepresents a predetermined percentage of the value of the rst directvoltage of waveform G as determined by the setting of the shaft 33. Adial 34 and pointer 35 coupled to shaft 33 may be calibrated in terms ofpercent of angular rotation of shaft 33 such that when potentiometer 31produces a second output voltage whose magnitude is equal to themagnitude of the first direct voltage the dial 34 indicates 100 percent.When potentiometer 31 produces zero output voltage, the dial 34 indi-Thus, where the linear potentiometer 31 is of the continuously rotatabletype, one turn of shaft 33 represents 100% of the magnitude of the firstvdirect output voltage of waveform G. Accordingly, one

turn of shaft 33 may be considered as representing the distance betweenlines a and b on chart 18 as measured along the line of scan, and thisrelation is maintained regardless of the spacing between these lines.

An error control voltage whose magnitude varies according to thedifference between the second direct voltage of waveform H and the thirddirect voltage of waveform I is produced for controlling the position ofphotoscanner 10 along its direction of scan with respect to lines a andb. This error control voltage is obtained assigns from the movablecontact 38 of relayk comparator 39. The second direct voltage issupplied tofixed contact 40 of relay. 39 and the third direct voltage issupplied to fixed contact 41. The movable contact 38 alternates betweencontacts 40 and 41 at the frequency of the alternating switching voltagesupplied to relay winding 42. For the condition when the magnitude ofthe third direct voltage exceeds the magnitude of the second directvoltage, the voltage at movable contact 38 appears as Waveform. J ofFig. 3. This voltage is coupled to the filter and servo amplifier 43 toproduce the sinusoidal error control voltage of waveform K. The phase ofthis error control voltage is determined by the larger of the second andthird direct voltages and the amplitude is determined by the differencebetween the second. and third direct voltages.

The error control voltage is coupled through position 1 of switch 44 andover lead 45 to a Servomotor 46. An alternating voltage from the samesource as the alternating switching voltage is supplied as a referencevoltage to Servomotor 46. The error control voltage of Waveform Kenergizes Servomotor 46 to drive the position of photoscanner along itsdirection of scan through rack 47 and pinion 48 until the error controlvoltage reduces to Zero.

The position occupied by the photoscanner with respect to lines a and bwhen the error control voltage of waveform K has been reduced to zero isdetermined by the angular position of shaft 33. A setting of shaft 33 toan angular position corresponding to one-quarter or 25 percent of oneturn sets the value of the seconddirect voltage of waveform H at 25percent of the magnitude tof the first direct voltage of waveform G. Themagnitude of the second direct voltage thus corresponds to a distanceequal to 25 percent of the total distance between lines a and b asmeasured along the line of scan relative to line zz. Accordingly, thesetting or angular position of shaft 33 as read from dial 34 correspondsto an imaginary line d on chart 18. Thus, the position c correspondingto the center of scan of photoscanner 1) can be automatically moved bythe servo control system to correspond to any position between the linesa and b, such as line d, as determined by shaft 33. In other words, theposition c corresponding to the center of scan of the photoscanner 10can be automatically adjusted under the control of shaft 33 tointerpolate by any selected percentage on dial 34 a predeterminedposition situated between lines a and b, and this interpolated positionis independent of the distance between lines a and b.

The photoscanning system of Fig. l may be arranged to interpolatebetween adjacent pairs of loran lines of position Where the lines a andb on chart 18 represent the loran lines between which a craft islocated. Where these loran lines are spaced apart by a distancecorresponding to a certain fixed time difference interval, for example100 microseconds, th-e shaft 33 must be properly geared and indexed tothe input data representing the measured loran number or time differenceso that one revolution of shaft 33 corresponds to a change in timedifference of 100 microseconds. A direct reading loran receiver such asthe Mark II loran manufactured by the Sperry Gyroscope Company Divisionof the Sperry Rand Corporation indicates the measured time differencebetween the arrival of master and slave pulses as a number on amechanically driven revolution counter. Accordingly, the mechanicalshaft driving this revolution counter may be coupled through appropriate`gearing so that a 1U() microsecond change in the time difference asread on the revolution counter corresponds to one turn of shaft 33. Forexample, assume that the position of a craft to be navigated by means ofthe loran system is situated between two adjacent lines of position, oneline corresponding to a time difference of 2600 microseconds and theother line corresponding to 2700 microseconds.

Where line a on chart 18r corresponds to, the loran line representing26.00 microseconds when the angular position of shaft 33 indicates zerokpercent and line b corresponds to the loran line representing 2700ymicroseconds when the angular position of shaft 33 indicates 100percent, any intermediate angular position of shaft 33 corre- Spondingto the position of the craft between the two loran lines establishes animaginary predeterminedk line of position on chart 18 to which thecenter of scan of the photoscanner will be automatically moved, Thus,the position of the center of scan c withrespect to` chart 18 representsthe position of the craft between the loran lines.

Where it is desired to produce a shaft positioncorresponding to aposition on chart 18 between lines a and b to which the center of scanof photoscanner 10 already has been positioned, a second servo controlsystem including Servomotor 49 has been provided. The error controlvoltage of waveform K is coupled through position 2 of switch 44 toenergize Servomotor 49 to drive shaft 33 through gears 50 and 5 1 to anangular position representing the position of photoscanner 10.Servomotor 49 is supplied with a reference voltage from the same sourceas the reference voltage to Servomotor 46. Under this alternativeembodiment of the invention, input datafrom a loran receiver is notsupplied to shaft 33 since the shaft now represents output data ratherthan input data.

The present invention is not limited in its application to a lorannavigation system but may be used where an automatic interpolationdevice is desired to automatically interpolate -between first andysecond spaced lines or points. The invention is not limited to the useof a photoscanner. Any type of scanner which produces recurrent outputpulses from lines being scanned may be employed. Furthermore, magnetictab 20 need not be attached to a point on the circumference of drum 12where a pulse is produced corresponding to the center of scan. The pulseproduced by magnetic tab 20 merely defines a refer-ence point along thepath scanned by the photoscanner. Thus, the reference pulse may begenerated before or after the center of scan. In suoh case, point c inFig. 1 will be a point fixed with respect to the photoscanner that willautomatically follow the imaginary line d, which corresponds to theposition of the craft with respect to the area.

The reference pulse defining a point along :the scan path may begenerated by means other than a magnetic tab. Thus any resistive,capacitive or magnetic pick-off fixed with respect to drum 12 might beutilized.

Where more than two lines are scanned it is not necessary that theselines lbe spaced equi-distant along the scanned path. In any instance,the first direct voltage produced by condenser 64 is proportional to anddependent only on `the distance between the lines which bound the spacein which interpolation is desired. The action of the pulse selectorinsures thatthis voltage is not affected by non-uniformity in thespacing of the lines being scanned.

Since many changes couldbe made in the above construction and manyapparently widely :different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description ork shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

1. Apparatus for automatically moving the position of a scanner withrespect to a predetermined position located between first and secondlines on a chart, said scanner transversely scanning said first andsecond lines at a constant scanning speed and producing first recurrentoutput pulses corresponding to the lines being scanned, the time betweensaid recurrent output pulses varying according to the distance betweensaid lines as measured along the line of scan, said scanner furtherproducing secondrecurrent output pulses whose time position occurs atthe center of each scanning cycle, comprising in combination, meansincluding a sawtooth generator means coupled to said scanner andresponsive to said first yrecurrent pulse for producing a linearsawtooth output voltage, the peak value of said sawtooth voltage varyingaccording to said distance between said first and second lines, meanscoupled to the output of said sawtooth generator means for producing =afirst direct output voltage varying according to the peak value of saidsawtooth voltage, voltage divider means coupled to the output of saidpeak voltage producing means for receiving said first direct `outputvoltage, said voltage divider means including a shaft means coupledthereto for controlling the amount of voltage division produced thereinaccording to the angular position of said shaft, the angular position ofsaid shaft corresponding to a predetermined position on said chartbetween said first and second lines, said voltage divider meansproducing a `second direct output voltage whose magnitude is determinedby the voltage division of said voltage divider means and correspondsyto the distance Ibetween one of said first or second lines on saidchart and said predetermined position on said chart between said firstand second lines as measured along the line of scan, switching meanscoupled to the output of said sawtooth generator means and to saidscanner and responsive to 4the coincidence of said linear sawtoothoutput voltage and said second recurrent center of scan pulses forproducing `a third direct output voltage equal to the instantaneousmagnitude of said sawtooth voltage at the instants of occurrence of saidcenter of scan pulses, the magnitude of said third direct output voltagecorresponding to the distance between said one line on said chart andthe center of scan of said scanner as measured along the line of scan,comparator` means coupled to the output of said voltage divider meansand to the output of said switching means and responsive to thedifference between said second direct output voltage and said thirddirect output voltage for producing an error control voltage, and servomeans coupled to said scanner and responsive to said error controlvoltage for automatically moving said scanner along a direction parallelto its direction of scan until the center of scan coincides with thepredetermined position on said chart between said first and second linesas determined by the adjustment of said voltage divider means under thecontrol of said shaft.

2. In a system for transversely scanning rst and second lines on achart, said system including a scanner producing first recurrent outputpulses corresponding to the lines being scanned and further producingsecond recurrent output pulses whose time position occurs at the centerof each scanning cycle, apparatus for producing an output voltage whosemagnitude is proportional to the distance between one of said first orsecond lines on said chart and a position on said chart between saidlines corresponding to the center of scan of said scanner, said distancebeing measured along the line of scan of said scanner, comprising incombination, means coupled to the output of said scanner and responsiveto said first recur-rent output pulses for producing -a linear sawtoothoutput voltage, the peak value of said sawtooth voltage varyingaccording to the distance between said first and second lines asmeasured along the line of scan, and electronic switching means coupledto the output ot' said sawtooth voltage producing means and to theoutput of said scanner and responsive to the coincidence of saidsawtooth output voltage and said second recurrent center of scan pulses,said electronic switching means producing a direct output voltage equalto ythe instantaneous magnitude of said sawtooth voltage at the instantsof occurrence of said center of scan pulses, the magnitude of saiddirect output voltage corresponding to said distance between one of saidlines on said chart and the center of scan of said scanner.

3. Photo-responsive apparatus comprising in combination, a photoscannerfor transversely scanning first and second uniformly illuminated lineson a chart at a constant scanning speed, said photoscanner producingfirst recurrent output pulses corresponding to the lines being scanned,the time between said recurrent output pulses varying according to theseparation between said lines, said photoscanner further producingsecond recurrent output pulses whose time position occurs at the centerof each scanning cycle, means for automatically moving said photoscannerin a direction parallel to its direction of scan for positioning thecenter of scan of said photoscanner relative to a predetermined positionon said chart located between said first and second lines, said meansincluding a sawtooth generator means coupled to said photoscanner andresponsiver to said first recurrent pulses for producing a linearsawtooth output voltage, the peak value of said sawtooth voltage varyingaccording to the separation between said first and second lines, meanscoupled to the output of said sawtooth generator means for producing afirst direct output voltage varying according to the peak value of saidsawtooth voltage, adjustable voltage divider means coupled to the outputof said peak voltage producing means for receiving said first directoutput voltage, said voltage divider means including means for adjustingthe amount of voltage division produced therein, said adjustable voltagedivider means producing a second direct output voltage whose magnitudeis determined by the adjustment of said voltage divider means, themagnitude of said second direct output voltage corresponding to thespacing between one of said first or second lines and a predeterminedposition on said chart between said first and second lines', switchingmeans coupled to the output of said sawtooth generator means and to saidphotoscanner and responsive to the coincidence of said linear sawtoothoutput voltage and said second recurrent center of scan pulses forproducing a third direct output voltage equal to the instantaneousmagnitude of said sawtooth voltage at the instants of occurrence of saidcenter of scan pulses, the magnitude of said third direct output voltagecorresponding to the spacing between said one line on said chart and thecenter of scan of said photoscanner, comparator means coupled to theoutput of said adjustable voltage divider means and to the output ofsaid switching means and responsive to the difference between saidsecond direct output voltage and said third direct output voltage forproducing an error control voltage, and servo means coupled to saidphotoscanner and responsive to said error control voltage forautomatically moving said photoscanner along its direction of scan untilthe center of scan coincides with the predetermined position on saidchart between said first and second lines as determined by theadjustment of said voltage divider means.

4. ln apparatus for transversely scanning first and second lines on achart, said apparatus including a scanner recurrently scanning saidfirst and second lines and producing first recurrent output pulses assaid lines are being scanned, the time difference between said firstrecurrent output pulses varying according to the separation between saidlines, said scanner further producing second recurrent output pulseswhose time position occurs at the center of each scanning cycle, meansfor producing an output control voltage whose magnitude is determined bythe difference between a position on said chart corresponding to thecenter of scan of said scanner system and a predetermined position onsaid chart located between said first and second lines, and whosepolarity is determined by the direction of the center of scan of saidscanner relative to said predetermined position on said chart,comprising in combination, a sawtooth generator means coupled to saidscanner and responsive to said first recurrent output pulses forproducing a linear sawtooth output voltage, the peak value of saidsawtooth voltage varying according to the separation between acoge/is 9said first and second lines, means coupled to the output of saidsawtooth generator means for producing a first direct output voltagevarying according to the peak value of said sawtooth voltage, adjustablevoltage divider means coupled to the output of said peak voltageproducing means and responsive to said peak voltage for producing asecond direct output voltage whose magnitude corresponds to the spacingbetween one of said first r second lines and a predetermined position onsaid chart located between said first and second lines, switching meanscoupled to the output or" said sawtooth generator means and to saidscanner and responsive to the magnitude of said sawtooth output voltageat the instants of occurrence of each of said second recurrent center ofscan pulses, said switching means producing a third direct outputvoltage equal to the instantaneous magnitude of said sawtooth voltage atthe occurrence of each center pf scan pulse, and means coupled to theoutput of said adjustable voltage divider means and said switching meansfor producing an output control voltage whose magnitude is determined bythe difference between said second direct output voltage and said thirddirect output voltage, the magnitude of said output control voltagevarying according to the difference between the center of scan of saidscanner and said predetermined position.

5. Apparatus for automatically interpolating between first and secondspaced lines on a chart comprising in combination, a scanner tranverselyscanning said lines, said scanner producing first recurrent pulsescorresponding to the lines being scanned, means coupled to said scannerand responsive to said first recurrent pulses for producing a firstdirect output voltage whose magnitude varies according to the distancebetween said first and .second lines as measured along the line of scan,said scanner further producing second recurrent output pulses whose timeposition occurs at the center of each scanning cycle, adjustable voltagedivider means coupled to the output of said means producing said firstdirect output voltage, means coupled to said adjustable voltage dividermeans for setting the amount of voltage division produced therein, saidvoltage divider means producing a second direct output voltage whosemagnitude varies according to the distance between one of the lines onsaid chart and a predetermined position on said chart between saidlines, said predetermined position being determined by the setting ofsaid voltage divider means, means coupled to said scanner and responsiveto said first recurrent pulses and said Second recurrent center of scanpulses for producing a third direct output voltage whose magnitudevaries according to the distance between said one line on said chart andthe center of scan of said scanner as measured along the line of scan,and means responsive to the diierence between said second and thirddirect voltages for controlling the relative position between the centerof scan of said scanner and said predetermined position on said chartbetween said first and second lines.

6. Apparatus for automatically controlling the angular position of ashaft means in accordance with the position of the center of scan of ascanner, comprising in combination, a scanner transversely scanningfirst and second spaced lines on a chart and producing first recurrentpulses corresponding to the lines being scanned, means coupled to saidscanner and responsive to said first recurrent pulses for producing arst direct output voltage whose magnitude varies according to thedistance between said first and second lines as measured along the lineof scan, said scanner further producing a second recurrent output pulsewhose time position occurs at the center of each scanning cycle, voltagedivider means coupled to the output of said means producing said firstdirect output voltage, shaft means coupled to said voltage divider meansfor setting the amount of voltage division produced therein according tothe angular position of said shaft means, said voltage divider meansproducing a second direct output voltage whose magnitude variedaccording to the distance between one of the lines on said shaft and apredetermined position on said chart between said lines, means coupledto said scanner and responsive to said first recurrent pulses and saidsecond recurrent center of scan pulses for producing a third directoutput voltage whose magnitude varies according to the distance betweensaid one line on said chart and the center of scan of said scanner asmeasured along the line of scan, and means responsive to the differencebetween said second and third direct voltages for controlling theangular position of said shaft means and setting said voltage divider sothat said second direct voltage is substantially equal in magnitude tosaid third direct voltage, the angular position of said shaft meanscorresponding to the position of the center of scan of said scannerbetween said first and second lines.

7. Apparatus for automatically moving the position of a scanner withrespect to a predetermined position located between first and secondlines on a chart, said scanner transversely scanning said first andsecond lines and producing first recurrent output pulses correspondingto the lines being scanned, said scanner further producing secondrecurrent output pulses whose time position occurs at the center of eachscanning cycle, comprising in combination, means coupled to said scannerand responsive to said first recurrent pulses for producing a linearsawtooth output voltage, means coupled to said sawtooth voltageproducing means for producing a first direct o-utput Voltage whosemagnitude varies according to the distance between said rst and secondlines as measured along the line of scan, adjustable voltage dividermeans coupled to the output of said means producing said first directoutput voltage, means coupled to said adjustable voltage divider meansfor setting the amount of voltage division produced therein, saidvoltage divider means producing a second direct output voltage whosemagniture varies according to the distance between one of the lines onsaid chart and a predetermined position on said chart between saidlines, said predetermined position being determined by the setting ofsaid voltage divider means, means coupled to the output of said voltagedivider means and to said sawtooth voltage producing means, said meansbeing further coupled to said scanner for receiving said secondrecurrent pulses, said means being responsive to the difference betweenthe magnitude of said second direct output voltage and the magnitude ofsaid sawtooth voltage at the instants of occurrence of said secondrecurrent center of scan pulses from said scanner for producing an errorcontrol output voltage, said error control output voltage varying inmagnitude according to the distance between the predetermined positionon said chart between said lines and the center of scan position of saidscanner, and means responsive to said error control output voltage forcontrolling the position of said scanner relative to said predeterminedposition on said chart between said first and second lines.

8. A photoscanner comprising a phototube having a photosensitive cathodetherein, a mask disposed opposite said photosensitive cathode, said maskhaving a narrow elongated slit therethrough for admitting light to saidphotosensitive cathode, a hollow cylindrical drum surrounding saidphototube, said hollow cylindrical drum having an opening through thewall thereof in the form of a helical slit about the longitudinal axisof said drum, means coupled to said cylindrical drum for rotating saiddrum about its longitudinal axis, the longitudinal axis of said drumextending parallel to the narrow elongated slit in said mask7 thehelical slit in said rotating cylindrical drum and the elongated slit insaid mask cooperating to admit a scanning beam of light upon saidphotosensitive cathode, and means affixed to said drum for producing anoutput signal whose time of occurrence corresponds to a predeterminedpoint in the scanning cycle of said photoscanner.

' 9. A photoscanner comprising a phototube having a photosensitivecathode therein, a mask disposed adjacent said photosensitive cathode,said mask having a narrow elongated slit therethrough for admittinglight to said photosensitive cathode, a hollow cylindrical drumsurrounding said phototube and mask, said hollow cylindrical drum havingan opening through the wall thereof in the form of a helical slit aboutthe longitudinal axis of said drum, said means coupled to saidcylindrical drum for rotating said drum about its longitudinal axis, thelongitudinal axis of said drum extending parallel to the narrowelongated slit in said mask, the helical slit in said rotatingcylindrical drum and the elongated slit in said mask cooperating toadmit a scanning beam of light upon said photosensitive cathode, andmeans affixed to said drum for producing an output signal whose time ofoccurrence corresponds to the center of scan of said photoscanner.

10. Apparatus for automatically locating a photoscanner with respect toa chart representing an area to correspond with the position of a pointwith respect to said area, the position of said point with respect tosaid area being determined by its location relative to an arbitrarycoordinate system fixed with respect to said area, said` coordinatesystem comprising at least one set of nonintersecting lines, said chartbeing illuminated and having superimposed thereon a plurality ofnonintersecting lines corresponding to said coordinate lines, saidapparatus receiving an input signal representing a first ratio equal tothe distance of said point from an adjacent coordinate line divided bythe distance between the two coordinate lines adjacent said point, saidphotoscanner having photosensitive means for producing an outputelectrical signal in accordance with the amount of light received and adirective means for directing light received from an elemental area ofthe chart upon said photosensitive means, the orientation of thedirective means being recurrently varied, whereby said photosensitivemeans receives light recurrently and successively from a series ofcontiguous elemental areas defining a locus transverse to said chartlines, and whereby the output signal of the photosensitive meansconsists of recurrent groups of first pulses corresponding to the chartlines, said groups being recurrent at the frequency of variation of theorientation of the directive means and the time between pulses of agroup corresponding to the spacing of the chart lines along said locus,comprising in combination, a reference pulse generator for generatingreference pulses recurrent at the frequency of variation of theorientation of the directive means, said reference pulses having atemporal relationship to the pulses of said groups corresponding to thelocation of the photoscanner with respect to the chart lines, a sawtoothgenerator coupled to the photoscanner and responsive to said iirstpulses for generating a linear sawtooth voltage wave, first samplingmeans coupled to the sawtooth generator and responsive to said sawtoothvoltage wave for producing a first direct voltage having a magnitudeequal to the peak magnitude of the individual sawtooth cycle generatedduring the interval between the pair of first pulses occurringimmediately before and immediately after a reference pulse,proportioning means responsive to said input signal and coupled to thefirst sampling means for receiving said first direct voltage and fordelivering a second direct voltage bearing a ratio to said first `directvoltage equal to said first ratio, second sampling means for producing athird direct voltage equal to the instantaneous magnitude of a voltagewave received at a first input terminal when said second sampling meansis triggered by a pulse applied to a second input terminal, said firstinput terminal being coupled to the sawtooth generator lfor receivingsaid sawtooth voltage wave, said second input terminal being coupled tothe reference pulse generator for receiving said reference pulses,comparator means for producing an error control voltage corresponding tothe difference between a. pair of 12 input direct voltages, saidcomparator means being coupled to the proportioning means and to thesecond sampling means to receive said second and third voltages, andservomechanism means coupled to the photoscanner and responsive to saiderror control voltage for auto- 'matically moving the photoscanner todecrease the magnitude of the error control voltage.

1l. Apparatus for automatically locating a photoscanner with respect toa chart representing an area to correspond with the position of a craftwith respect to said area, the position of said craft with respect tosaid area being determined by its location relative to an arbitrarycoordinate system fixed with respect to said area, said coordinatesystem comprising at least one set of nonintersecting lines, said chartbeing illuminated and having superimposed thereon a plurality ofnonintersecting lines corresponding to said coordinate lines, saidapparatus receiving an input signal representing a first ratio equal tothe distance of said craft from an adjacent coordinate line divided bythe `distance between the two coordinate lines adjacent said craft, saidphotoscanner having photosensitive means for producing an outputelectrical signal in accordance with the amount of light received and a`directive means for directing light received from an elemental area ofthe chart upon said photosensitive means, the orientation of thedirective means being recurrently varied, whereby said photosensitivemeans receives light recurrently and successively from a series ofcontiguous elemental areas defining a locus transverse to said chartlines, and whereby the output signal of the photosensitive meansconsists of recurrent groups of first pulses corresponding to the chartlines, said groups being recurrent at the frequency of variation of theorientation ofthe directive means and the time between pulses of a groupcorresponding to the spacing of the chart lines along said locus,comprising in combination, a reference pulse generator for generatingreference pulses recurrent at the frequency of variation of theorientation of the directive means, said reference pulses having atemporal relationship to the pulses of said groups corresponding to thelocation of the photoscanner with respect to the chart lines, delaymeans coupled to said photoscanner for producing an output signalconsisting of recurrent groups of second pulses corresponding to thechart lines, said second pulses lagging said first pulses by a timesmall compared to the time between any two successive first pulses, asawtooth generator coupled to said delay means and responsive to saidsecond pulses for generating a linear saw.- tooth voltage wave, a pulseselector means coupled to said photoscanner and to said reference pulsegenerator and responsive to said reference pulses for producing gatingpulses simultaneously with the first pulses immediately following saidreference pulses, first sampling means coupled to the sawtooth generatorand to the pulse selector and responsive to said gating pulses forproducing a rst direct voltage having a magnitude equal to the peakmagnitude of the individual sawtooth voltage cycle corresponding to saidgating pulse, proportioning means responsive to said input signal andcoupled to the first sampling means lfor receiving said first directvoltage and for delivering a second direct voltage bearing a ratio tosaid first direct voltage equal to said first ratio, second samplingmeans for producing a third direct voltage equal to the instantaneousmagnitude of a voltage wave received at a first input terminal when saidsecond sarnpling means is triggered by a pulse applied to a second inputterminal, said first input terminal being coupled to the sawtoothgenerator for receiving said sawtooth voltage wave, said second inputterminal being coupled to the reference pulse generator for receivingsaid reference pulses, comparator means for producing an error controlvoltage corresponding to the difference between a pair of input directvoltages, said comparator means being coupled to the proportioning meansand to the second sampling means to receive said second and thirdvoltages;

13 and servomechanism means coupled to the photoscanner and responsiveto said error control voltage for automatically moving the photoscannerto decrease the magnitude of the error control voltage.

12. Apparatus for automatically locating a photoscanner with respect toa chart representing an area to correspond with the position of a craftwith respect to said area, the position of said craft with respect tosaid area being determined by its location relative to an arbitrarycoordinate system fixed with respect to said area, said coordinatesystem comprising at least one set of nonintersecting lines, said chartbeing illuminated and havin-g superimposed thereon a plurality ofnonintersecting lines correspondingV to said coordinate lines, saidapparatus receiving an input signal representing a rst ratio equal tothe distance of said craft from an adjacent coordinate line divided bythe distance between the two coordinate lines adjacent said craft, saidphotoscanner having photosensitive means for producing an outputelectrical signal in accordance with the amount of light received and adirective means for directing light received from an elemental arca of-the chart upon said photosensitive means, the orientation of thedirective means being re- Acurrently varied, whereby said photosensitivemeans receives light recurrently and successively from a series of-contiguous elemental areas defining a locus transverse to said chartlines, and whereby the output signal of the photosensitive meansconsists of recurrent groups of rst pulses corresponding to the chartlines, said groups being recurrent at the frequency of variation of theorientation -of` the directive means and the time between pulses of agroup corresponding to the spacing of the chart lines along said locus,comprising in combination, a reference pulse generator for generatingreference pulses recurrent at the frequency of variation of theorientation of the directive means, said reference pulses having atemporal relationship to the pulses of said groups corresponding to thelocation of the photoscanner with respect to the chart lines, a sawtoothgenerator coupled to the photoscanner and responsive to said firstpulses for generating a linear sawtooth voltage wave, first samplingmeans coupled to the sawtooth generator and responsive to said sawtoothvoltage wave for producing a first direct voltage having a magnitudeequal to the peak magnitude of the individual sawtooth cycle generatedduring the interval between the pair of first pulses occurringirnvmediately before and immediately after a reference pulse, voltagedivider means coupled to said first sampling means for receiving saidfirst direct voltage, said voltage divider means including a shaft forcontrolling the amount of voltage division produced therein according tothe angular position of said shaft, the angular position of said shaftcorresponding to said input signal, said voltage divider means producinga second direct voltage bearing a ratio to said first direct voltageequal to said first ratio, second sampling means for producing a thirddirect voltage equal to the instantaneous magnitude of a voltage wavereceived at a first input terminal when said second sampling means istriggered by a pulse applied to a second input terminal, said firstinput terminal being coupled to the sawtooth generator for receivingsaid sawtooth voltage wave, said second input terminal being coupled tothe reference pulse generator for receiving said reference pulses,comparator means for producing an error control voltage corresponding tothe difference between a pair of ir put direct voltages, said comparatormeans being coupled to the proportioning means and to the secondsampling means to receive said second and third voltages, andservo-mechanism means coupled to the photoscanner and responsive to saiderror control voltage for automatically moving the photoscanner todecrease the magnitude of the error control voltage.

13. Apparatus for comparing the location of a photoscanner with respectto a chart representing an area to the position of a point with respectto said area, the

position `of said point with respect to said area being determined byits location relative to an arbitrary coordinate system fixed withrespect to said area, said coordinate systern comprising at least oneset of lines, said chart being illuminated and having superimposedthereon a plurality of lines corresponding to said coordinate lines,said apparatus receiving an input signal representing a first ratioequal to the distance of said point from an adjacent coordinate linedivided by the distance between the two coordinate lines adjacent saidpoint, said photoscanner having photosensitive means for producing anoutput electrical signal in accordance with -the amount of lightreceived and a directive means for directing light received from anelemental area of the chart upon said photosensitive means, theorientation of the directive means `being recurrently varied, wherebysaid photosensitive means receives light recurrently and successivelyfrom a series of contigmous elemental areas defining a locus transverseto said chart lines, and whereby the output signal of the photosensitivemeans consists of recurrent `groups of first pulses corresponding to thechart lines, said groups vbeing recurrent at the frequency of variationof the orientation of the directive means and the time between pulses ofa group corresponding to the spacing of the :chart lines along saidlocus, comprising in combination, a reference pulse generator forgenerating reference pulses recurrent at the frequency of variation ofthe orientation of ,the directive means, said reference pulses have atemporal relationship to the pulses of said groups corresponding to thelocation of the photoscanner with respect to the chart lines, means forproducing a first direct voltage having a magnitude proportional to thedistance between the pair of lines corresponding to the pair of firstpulses occurring immediately before and immediately after a referencepulse, proportioning means coupled to receive said first direct voltageand responsive to said input signal for producing a second directvoltage bearing a ratio to said first direct voltage equal to said firstratio, means for producing a third direct voltage proportional to theposition of said photoscanner with respect to said chart lines, andcomparator means for producing an error voltage corresponding to thedifference between a pair of received direct voltages, said comparatormeans being adapted to receive said second and third voltages.

14. Apparatus for automatically representing the position of a craftwith respect to an area on a chart representing said area, the positionof said craft with respect to said area being determined by its locationrelative to an arbitrary coordinate system fixed with respect to saidarea, said coordinate system comprising at least one set ofnon-intersecting lines, said chart being illuminated and havingsuperimposed thereon a plurality of nonintersecting lines correspondingto said coordinate lines, said apparatus receiving an input signalrepresenting a first ratio equal to the distance of said craft from anadjacent coordinate line divided by the distance between the twocoordinate lines adjacent said craft, comprising a pho-toscanner havingphotosensitive means for producing an output electrical signal inaccordance with the amount of light received and a directive means fordirecting light received from an elemental area of the chart upon saidphotosensitive means, the orientation of the directive means beingrecurrently varied, whereby said photosensitive means receives lightrecurrently and successively from a series of contiguous elemental areasdefining a locus transverse to said chart lines, and whereby the outputsignal of the photosensitive means consists of recurrent groups of firstpulses corresponding to the chart lines, said groups being recurrent atthe frequency of variation of the orientation of the directive means andthe time between pulses of a group corresponding to the spacing of thechart lines along said locus, a reference pulse generator for generatingreference pulses recurrent at the frequency of variation of theorientation of the directive means, said reference pulses having atemporal relationship to the pulses of said groups corresponding to thelocation of the photoscanner with respect to the chart lines, a sawtoothgenerator coupled to the photoscanner and responsive to said firstpulses for generating a linear sawtooth voltage wave, first samplingmeans coupled to the sawtooth generator and responsive to said sawtoothvoltage wave for producing a first direct voltage having a magnitudeequal to the peak magnitude of the individual sawtooth cycle generatedduring the interval between the pair of first pulses occurringimmediately before and immediately after a reference pulse,proportioning means responsive to said input signal and coupled to thefirst sampling means for receiving said first direct voltage and fordelivering a second direct voltage bearing a ratio to said first directvoltage equal to said first ratio, second sampling means for producing athird direct voltage equal to the instantaneous magnitude of a voltagewave received at a first input terminal when said second sampling meansis triggered by a pulse applied to a second input terminal, said firstinput terminal being coupled to the sawtooth generator for receivingsaid sawtooth voltage wave, said second input terminal being coupled tothe reference pulse generator for receiving said reference pulses,comparator means for producing an error control voltage corresponding tothe difference between a pair of input direct voltages, said 'comparatormeans being coupled to the proportioning means and to the secondsampling means to receive said second and third voltages, andservomechanism means coupled to the photoscanner and responsive to saiderror control voltage for automatically moving the photoscanner todecrease the magnitude of the error control voltage.

l5. Apparatus for comparing the location of a scanning device withrespect to a chart representing an area to the position of a point withrespect to said area, the position of said point with respect to saidarea being determined by its location relative to an arbitrarycoordinate system fixed with respect to said area, said coordinatesystem comprising at least one set of lines, said chart havingsuperimposed thereon a plurality of lines corresponding to saidcoordinate lines, said apparatus receiving a first signal representing afirst ratio equal to the distance of said point from an adjacentcoordinate line divided by the distance between the two coordinate linesadjacent said point, comprising in combination, la scanning deviceadapted to periodically scan said chart along a path transverse to saidchart lines and to produce an output signal consisting of recurrentgroups of first pulses corresponding to said chart lines, said groupsbeing recurrent at the periodic scanning rate of said scanning deviceand the time between pulses of a group corresponding to the spacing ofthe chart lines along said path, a reference pulse generator forgenerating reference pulses recurrent at said scanning rate and having atemporal relationship to the pulses of said groups ycorresponding to therelationship of the location of a reference point fixed with respect tosaid scanning device to said chart lines, means for producing a secondsignal representing the distance between the chart lines adjacent saidreference point, means coupled to receive said second signal andresponsive to said first signal for producing a third signalrepresenting with respect to said second signal a ratio equal to saidfirst ratio, means for producing a fourth signal representing the ratiobetween the distance of said reference point from an adjacent chart lineto the distance between the pair of chart lines adjacent said referencepoint, and comparator means for producing an error signal correspondingto the difference between a pair of received signals, said comparatormeans being adapted to receive said third and fourth signals.

16. Apparatus for comparing the location of a scanning device withrespect to a chart representing an area to the position of a point withrespect to said area, the position of said point with respect to saidarea being dctrllned Iby its location relative to an anbitrarycoordinate system fixed with respect to said area, said coordinatesystem comprising at least one set of lines, said chart havingsuperimposed thereon a plurality of lines corresponding to saidcoordinate lines, said apparatus receiving a first signal representing afirst ratio equal to the distance of said point from an adjacentcoordinate line divided by the distance vbetween the two coordinatelines adjacent s'aid point, comprising in combination, a scanning deviceadapted to periodically scan said chart along a path transverse to saidchart lines and to produce an output signal consisting of recurrentgroups of first pulses correspond- -ing to said chart lines, said groupsbeing recurrent at the periodic scanning rate of said scanning deviceand the time 'between pulses of a group corresponding to the spacing ofthe chart lines along said path, a reference pulse generator forgenerating reference pulses recurrent at said scanning rate and having atemporal relationship to the pulses of said groups corresponding to therelationship of the location of a reference point fixed with respect tosaid scanning device to said chart lines, means for producing a secondsignal representing the time between the first pulses occurringimmediately before and immediately after a reference pulse, meanscoupled to receive said second signal and responsive to said firstsignal for producing a third signal representing with respect to saidsecond signal a ratio equal to said first ratio,

means for producing a fourth signal representing the ratio of the timebetween a reference pulse and the first pulse occurring immediatelybefore said reference pulse to the time between said first pulsesoccurring immediately before and immediately after said reference pulse,and comparator means for producing an error signal corresponding to thedifference between a pair of received signals, said comparator meansbeing adapted to receive said third and fourth signals.

17. Apparatus for comparing the location of a scanning device withrespect to a chart representing an area to the position of a point withrespect to said area, the position of said point with respect to saidarea being determined by its location relative to an arbitrarycoordinate system fixed with respect to said area, said coordinatesystem comprising at least one set of lines, said chart havingsuperimposed thereon a plurality of lines corresponding to saidcoordinate lines, said apparatus receiving a first signal representing afirst ratio equal to the distance of said point from an adjacentcoordinate line divided by the distance between the two coordinate linesadjacent said point, comprising in combination, a scanning deviceadapted to periodically scan said chart along a patli transverse to saidchart lines and to produce an output signal consisting of recurrentgroups of first pulses corresponding to said chart lines, said groupsbeing recurrent at the periodic scanning rate of said scanning deviceand the time 'between pulses of a group corresponding to the spacing ofthe chart lines along said path, a reference pulse generator forgenerating reference pulses recurren-t at said scanning rate and havinga temporal relationship to the pulses of said -groups corresponding tothe relationship of the location of a reference point fixed with respectto said scanning device to said chart lines, means adapted to receivesaid output signal and responsive to said first signal for producing asecond signal representing said first ratio, means adapted to receivesaidioutput signal and said reference pulses for producing a thirdsignal representing the ratio between the distance of said referencepoint from an adjacent chart line to the distance between the pair ofchart lines adjacent said reference point, and comparator means `forproducing an error signal corresponding to the difference between a pairof received signals, said comparator means being adapted t receive saidsecond and third signals. :Lf

18. Apparatus for comparing the location of a'frst point with respect toa first line family to the location of a second point with respect to asecond line family,

said apparatus receiving a first signal representing a first ratio equalto the distance of said second point from an adjacent line of saidsecond line family divided by the distance between the two lines of saidsecond line family adjacent said second point, comprising incom'bination, means for producing a second signal representing thedistance between the pair of lines of said rst line family adjacent saidfirst point, means coupled to receive said second signal and responsiveto said first signal for producing `a third signal representing withrespect to said second signal a ratio equal to said first ratio, meansfor producing a fourth signal representing the ratio between thedistance of said first point from an adjacent line of said first linefamily to the distance between the paix' of lines of said first linefamily adjacent said first point, and comparator means for producing anerror signal corresponding to the difference between a pair of receivedsignals, said comparator means being adapted to receive said third andfourth signals.

19. Apparatus for comparing the location of a first point with respect'to a first line family to the location of a second point with respectto a second line family, said apparatus receiving a first signalrepresenting a rst ratio equal to the distance of said second point froman `adjacent line of said second line family divided by the distancebetween the two lines of said second line family adjacent said `secondpoint, comprising in combination, means for producing a second signalrepresenting a second ratio equal to the distance of said first pointfrom an adjacent line of said rst line family divided by the distancebetween the two lines of said first line family adjacent said firstpoint, and comparator means for producing an error signal `correspondingto the difference between a pair of received signals, said comparatormeans being adapted to receive said first and second signals.

20. Apparatus for automatically locating a device with respect to afirst line family to correspond with the location of Ia point withrespect to a second line family, said apparatus receiving a first`signal representing a Erst ratio equal to the distance of said pointfrom an adjacent line of said second line family divided by the distancebetween the two lines of said second line family adjacent said point,comprising in combination, means for producing a second signalrepresenting a second ratio equal to the distance of a reference pointfixed with respect to said device from an adjacent line of said firstline family divided by the distance between the two lines of said firstline family adjacent said reference point, comparator means forproducing an error signal corresponding to the difference between a pairof received signals, said comparator means being adapted to receive saidfirst and second signals, and positioning means mechanically coupled tosaid device and responsive to said error signal for automatically movingsaid device to decrease the malgnitude of said error signal.

La Pierre Mar. 20, 1945 McLennan Nov. 29, 1949 EHR ` UNITED STATESPATENT oEEIcE CERTIFICATE OE CORRECTION Patent Noo 2,892,9f'8 June BOQ19559? Wilbert P0 Frantz Column 4, line' O9 for' "magniutde" read mmagnitude Column 8,., line iy for' "1'esponsiveT" :read :m Te'sponsive'ma; column l0,9 lili@ "shaft" read @hart mo Signed and Sealed this 29thday of March 19600 (SEAL) Attest;

KARL IID AXLINE ROBERT C. WATSON Attesting Ofcer I Commissioner ofPatents UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent Noo2,892,98 June 3Q, 3.959

Wilbert Po Frantz Column 4, line' AO, for' "magniutdw line' 16, for"T'esponsiver" "shaft" read Chart read m- Tic-sponsive4 m5 Column lQlili@ Signed and Sealed this 29th day ofA March 1960.,

(SEAL) Attest:

Commissioner of Patents

